1. Field of the Invention
The present invention relates to an apparatus and method for maintaining proper alignment between platens of a mold clamp for a molding machine and, more particularly, to the use of electromagnetic sensors to detect misalignment of the platens at all stages of the molding process.
2. Description of the Related Art
Very large molding machines use platens which, if misaligned when moving, can cause substantial mechanical damage to the machine or the mold installed in it. The problem of maintaining platen parallelism or "leveling" during clamping operations for processes like stamping metals, compression molding, or injection molding is well-known.
U.S. Pat. No. 3,640,660 issued to De Mets (incorporated herein by reference) discloses a vertical press with a means for measuring the relative distance between its two pressure platens when the platens are in a closed operative position. U.S. Pat. No. 5,196,150 issued to Mimura, et al. (incorporated herein by reference) discloses another vertical press in which the stroke deviation for the compression can be adjusted by detecting the position of the moving platen during the compression stroke so that levelness of the moving die can be maintained during the compression stroke. U.S. Pat. No. 5,314,327 issued to Stein and U.S. Pat. No. 5,454,709 issued to Leonhartsberger, et al. (both incorporated herein by reference) disclose a horizontal clamp with a moving platen having adjustable means for maintaining parallelism between the platens. These means are mechanical and need to be manually adjusted. Neither of these patents discloses means for sensing lack of parallelism automatically.
None of the above-referenced patents teach how misalignment of platens can be detected at any point over the entire operating stroke of the moving platen. The prior art teaches how misalignment can be detected and corrected only after the moving platen has closed and is being subjected to molding pressure, which subsequently causes the misalignment.
Causes of misalignment other than molding pressure, however, can cause the moving platen to become misaligned prior to the time the platens are closed. For example, a molded part may not eject properly from the mold and thus become trapped between the two mold halves as the moving platen closes the mold. If this entrapment is on one side of the mold only, a significant out of balance force will be applied to the moving platen causing it to cock or become seriously misaligned while still moving.
Another cause of misalignment could be the malfunction of a robot or part removal system in such a way that the robot or part of its tooling does not clear out of the path of the moving platen or the mold attached thereto. Collision between the robot or part of its tooling and the moving platen or mold could cause a misalignment that would go undetected in prior art devices.
Accordingly, there is a need in the art for a way to detect misalignment during the operating stroke of the moving platen, and promptly correcting such misalignment as soon as it is detected and before any damage is caused.